[F:1][C:2]1[CH:18]=[C:17]([F:19])[CH:16]=[CH:15][C:3]=1[CH2:4][CH:5]1[CH2:10][CH:9]([C:11]([O:13][CH3:14])=[O:12])[CH2:8][CH2:7][NH:6]1.CCN(C(C)C)C(C)C.[C:29](Cl)(=[O:32])[O:30][CH3:31].Cl>C(Cl)Cl.CC(OC)(C)C>[F:1][C:2]1[CH:18]=[C:17]([F:19])[CH:16]=[CH:15][C:3]=1[CH2:4][CH:5]1[CH2:10][CH:9]([C:11]([O:13][CH3:14])=[O:12])[CH2:8][CH2:7][N:6]1[C:29]([O:30][CH3:31])=[O:32]
To a solution of methyl 2-(2,4-difluorobenzyl)piperidine-4-carboxylate (7.1 g, 26.37 mmol) in DCM (100 mL) was added DIPEA (6.5 mL, 37.32 mmol) followed by methyl carbonochloridate (2.3 mL, 29.21 mmol) dropwise. After completed addition the reaction mixture was stirred at room temperature for 4 h, then 2 M HCl was added. The organic layer was diluted with MTBE, the biphasic mixture was filtered to remove insolubles and after phase separation the organic layer was washed with brine and satd NaHCO3, dried over MgSO4 and evaporated to give dimethyl 2-(2,4-difluorobenzyl)piperidine-1,4-dicarboxylate (8.51 g, 99%) as a dark oil. MS m/z 328 (M+H)+
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